Heat related chassis rattle help

[rtg]

In my 2018 GT PP1 I have a reasonably loud rattle, metal on metal sound, in the rear but only when the car is thoroughly warmed up. Like 30-45 minutes of constant driving. Once car cools down no rattle at all.

Not sure if related to mods but...

Mods are:

BMR IRS Lockout

BMR Rear Toe Ends

Eibach Pro-Plus Kit, lowering springs and sway bars

DSS Half Shafts

Alignment post spring install

If anyone has had a similar situation please let me know what you found. Trying to get an idea as to where to look. So far I have not found any that appears to need tightening. However, the car is not at high temp by the time I get it up in the air.

Thanks in advance,

Rob

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[Norm Peterson]

My guess is that it's related to thermal expansion of the exhaust system, allowing light contact somewhere once it gets hot enough. Exhaust systems are resiliently mounted, so they move around a little as you drive.


Norm

 

[rtg]

That's a possibility. I should have mentioned that an x-pipe was also added. However, when I was under there I checked for exhaust clearances and looked good all around with plenty of gap. An expansion would have to be significant from what I saw. Maybe I missed something.....

Thanks for the reply.

Rob

 

[Norm Peterson]

Keep in mind the magnitude of this expansion - fully warmed up by sustained hard running it could easily be half an inch or more near the rear of the car (most people probably don't expect it to be anywhere near that much). Plus, if the axial expansion is constrained by the hangers (whether by bottomed-out OE hangers or badly placed additional hangers), the pipe will kind of "pop out of shape" either laterally or vertically following a shape change of least resistance in accommodating this expansion. And for much of the length you've got two pipes each of which is going to do its own thing somewhat independently of what the other pipe does.


Norm

 

[rtg]

Thanks again. I will certainly take a look there.

Rob

 

[Norm Peterson]

Check for any indications of out-of-shape deflections.


Norm

 

[rtg]

Check for any indications of out-of-shape deflections.


Norm

I am not sure what you mean by "indications of out-of-shape deflections". Do you mean metal on metal marks from hitting?

Thanks,

Rob

 

[Norm Peterson]

Anything that looks like contact was being made. Might be a mark or a shiny spot, or a thin spot in the paint.


Norm

 

[rtg]

Got it.

Thanks,

Rob

 

[rtg]

Well, I am reasonably convinced that it is not likely the exhaust. Went out at lunch and within 15 minutes the rattle was back. I took the opportunity to grab each exhaust tip and gave a good shake and nothing. I won't say 100% not exhaust I am thinking not likely.

I do not think it is drive line either as there is no rattling going in and out of gear or from reverse to forward or vice versa.

This leaves sway bar mounts and linkages, spring mounts, or dampers. Already checked toe ends.

I just don't see how time and/or temp is a factor in the above. Time and/or temp would point to exhaust.

Whatever it is it does seem to be happening sooner and does sound like something loose. So may be easier to pin down.

BTW, the rattle occurs with bumps in the road.

Thanks,

Rob

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