Strange grumbling off and on

[06Suparu]

This is different to me lol. Its the 05 n/a i just bought. New timing belt, head gaskets, exhaust front to rear. Car runs amazing and then all of a sudden it sounded like the exhaust was banging on something. Crawled under and muscled onto the exhaust like a gorilla and its not even close to hitting anything. Sound comes and goes. Doesnt matter if im in a turn or not. Doesnt change if i apply brakes. My first thought was rear diff or hub assembly but now im thinking driveshaft carrier bearing. I have a complete OB wagon to pull parts from but dont really feel like throwing parts at this like spaghetti until something sticks. I am befuddled.

[Guacamole]

If it sounds like a rapid rattling my 06 NA does this too. Can't find the source since it only really does it at 70mph, sounds like it's a rattle in the header's heat shield.

[06Suparu]

Not a heat shield..those are all gone lol.

[Guacamole]

Piston slap?

[06Suparu]

No it sounds like its coming from the back of the car..more or less. Engine runs fantastic.

[06Suparu]

Ok so i finally figured out what the noise was. All the times under the car trying to figure it out and it turns out that the very tip of the tailpipe was hitting the back of the trailer hitch but only when i ran it hard. I bent the edge of the tailpipe just a bit and no problem. It was really strange to see how much the exhaust system expanded and contracted. At least 1/2 an inch.

[mike-tracy]

Thanks for the follow-up. I noticed my exhaust tip was super close when I was installing the tow hitch. Haven't checked since.

[STEVEW]

That happened to me when I first put on my hitch too. It took a while to figure it out.