Noise in drag car

Back on 5-25 I ran 8 rds of racing, everything working proper. Put car in trailer and next morning roll car out, warm in place not moving. When called to lanes, start engine and back up and I have an intermittent rattle. Sounds like if you put two small 3/16” nuts in an empty soda can tape the top and shake it. Rattle comes and goes intermittently, and always very brief 1-3 second noise and then stops. Does it with car in motion forward / backward driving pits and return rd. Doesn’t do it in BO or on the track at WOT or shut down on track.

Changed oil immediately when it happened and found nothing unusual. Continued racing with this rattle noise for five events. The sixth event went 8 rds again with rattle noise still intermittently occurring. Put car away and next day warm in place in pits and when called to first rd no reverse, TB spool is stuck in VB.

Thinking this was my noise I replaced the converter, oil cooler and borrowed a trans same as mine that was freshened with less than 100 runs. When finished I had same rattle noise and a slight vibration in BO and on track. Checked balance on tires and they’re perfect.

I indexed the converter position and indexed the driveshaft and went to a T+T this morning. Same intermittent rattle noise, driving the pits, start / stop, forward/ backward for 15 minutes. Nothing makes sense. Loaded it up, came home. Started it up, drove in garage and changed oil with 30 runs on oil. Filtered the drained oil, nothing. Cut the filter, looks normal. Sending an oil sample for analysis.

When changing the trans I checked the flexplate bolts and looked at the flexplate for cracks. Looked ok. I ordered a new flexplate that arrived Friday and going to install it tomorrow.

I’ve checked every nut, bolt, heim, anything that could rattle.

The rattle noise is not apparent at idle or revving engine while stopped. Always intermittent when slight load driving forward/ backward, never coasting. One needs to have ear protection on (I use ear plugs and have worn them over 40 yrs in my daily job) and in the car to hear. It’s loud inside car without ear protection and you can’t hear it.

Like I posted, the rattle sounds like two small nuts in a soda can when you shake it. Any ideas or like experience? I’m going nuts!!!

did you check the flex plate to crank bolts. That is a weird one for sure

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did you check the flex plate to crank bolts

Yes, the six bolts holding the flexplate to crank were tight.

lol I'll keep thinking

To add insult to injury, after I had replaced the converter, trans and cooler I was only able to make one run when I stopped on the return road to take off my jacket and the starter solenoid failed. I was towed back and it was perfectly quiet in the car (a few normal minor squeeks) being towed leading me to believe the noise is Not in the chassis. Loaded it up and went home.

that is a tough one

I bet it is the starter bendix randomly hitting the flexplate. Why it does it with a load and not without I have no clue. Especially since the starter broke, may not be the solenoid.

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I bet it is the starter bendix randomly hitting the flexplate.

I took the starter (House of Payne) apart on the failed starter and the recoil spring on the starter drive assembly was perfect. The solenoid would kick the drive sprocket out and return, but the starter motor would not run as the solenoid contacts failed. Pushing the start button would give a loud “clunk” noise from the drive gear hitting the flexplate. I put a used solenoid on from an older ECAE starter and it ran the motor when tried.

Loose nut behind the wheel?? Yeah, I've got nothing.

ujoint in driveshaft. Few of the rollers maybe bad? Pull the caps and check the needles. Years back I would overtighten them and it would crush the needle bearings. Cause a clicking noise sometimes.

A cracked fleplate will also make this exact sound

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Few of the rollers maybe bad? Pull the caps and check the needles. Years back I would overtighten them and it would crush the needle bearings. Cause a clicking noise sometimes.

Following a vibration problem I felt after the new converter install and different transmission, I checked the tire balance that was still perfect. I indexed the converter position and removed the driveshaft. The ujoint caps going to the diff pinion yoke felt very smooth when rotated. I religiously torque the ujoint bolts to 16 ft lbs when installing, nothing more.

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A cracked fleplate will also make this exact sound

I’m praying that this is the problem and have a new ATI flexplate on the bench. The TCI flexplate that has been in for 7 yrs visually looked good from the ground with transmission out and bolts were tight when checked.

Are you running a vacuum pump? My Star pump rattles sometimes under certain situations. I think if the RPM is low enough, the vanes tend to rattle.

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Are you running a vacuum pump? My Star pump rattles sometimes under certain situations. I think if the RPM is low enough, the vanes tend to rattle.

I use EVAC

Other thought was our chevelle for whatever reason had a very "tin like" rattle from the cage after it was installed. So bad my dad hated it and filled the tubes with spray foam which quited it down. Could something come loose inside and be boucing around? Nutsert that was in a bar?

^^^^ Agreed that anything like this could be possible. Mine’s stripped inside other than the stock dash that’s gutted and FG doors. To me the very intermittent rattle sounds like it’s coming from the rear of the engine / trans bell area. It’s a noisy tin can inside when running, but this rattle is distinctively new and never there prior.

Definitely a puzzle. I am guessing there was no significant change in the car's performance before vs after the rattle started?

I can only recall one deal that I had that was maybe similar, not a real "tinny" sound but it was similar in being a rattle, and also that it was intermittent, and only did it under moderate load, it sounded like it was coming from the flex plate / converter area, and was only noticeable with my helmet on (which muffled the other noises a bit).
Chased it for a while, tried all the same stuff you did, and just lived with it for several races.
Toward end of the season, I was preparing for the bracket finals, and did some of the routine maintenance items that are less frequent, (for me like once a year or so). Replaced plugs and wires, cap & rotor all at once. The problem disappeared. Can't say if it was one of those, or just coincidence, but it never happened again. And the car ran exactly the same as it did before and during the problem. It got me wondering if it was a slight / partial misfire and the sound was coming out of the headers.
The rotor and cap looked fine, I kept them as spares. So I was kind of thinking a plug or wire may have been on it's way out.

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Definitely a puzzle. I am guessing there was no significant change in the car's performance before vs after the rattle started?

This is correct… the car still ET’s the same, but the rattle is un-nerving and easily heard wearing hearing protection (ear plugs for me over 40yrs daily at work) while driving.

I just finished changing out the TCI flexplate from 2019 with a new ATI model. I inspected the old flexplate with a magnifying glass and could not see any cracks. The new ATI flexplate is an excellent upgrade and much better quality. But I have my doubts that this is the problem. The only major thing left to change is the engine.

Way back in the 90's, I had torque converter bolts that were just a little bit too long. No clue how that happened. Had some noise whenever car was idling. don't remember noise while driving at any speed or any vibration, just a mild ticking. Broke two flexplates before noticing the bolts were tight, but not clamping down enough to the flexplate due to bottoming out in the torque converter. They tightened enough that it wasn't visibly apparent. Good luck.