Rumble coming from rear end?
 

So...I have an FR-S Automatic Transmission. This only happens when the car is cold, and only the first time I put it in drive.

I start the car in the morning, back out of my driveway, shift into drive. Now for the fist 10 - 20 feet of driving forward, I have what feels like a vibration possibly coming from the rear differential? It kinda feels like when you drive over a rumble strip, not nearly as violent as a rumble strip, similar, kinda like 10% of what a rumble strip is.

The car is fine after that...drives and performs flawlessly the rest of the day.

Any ideas what the hell is going on?

Most likely you park outside. If so, there's a good chance that your brake rotors are rusted over from the condensation of the night and that rumbling is the rust being worn off by the brake pads.

Any other theories?

This is most likely.

Try hitting your brakes lightly during those first few feet. If you feel them grab extra hard extra fast that is what's happening. If you don't feel this it doesn't mean that this isn't what's happening.

My Jeep's brakes suck. So when they get that extra bite after a little moisture it's extremely noticeable.

Another option I notice in cold weather is the tires. The tires sit in a position, then cool down and become harder. After driving a bit the tires "loosen" back up, and all is well. If it only does it the first 10-20 feet, don't worry about it. Chances are you'll notice it more in the winter. This is normal for cars.

Yeah I was going to suggest this as well. It definitely hasn't been cool lately though, but I used to have this happen on my WRX summer tires when it got cold out. It feels exactly like the OP is describing. Maybe low tire pressure could cause it?

Are you doing 90 degree turns? When I leave my road it's like the diff is locking completely up.

I agree. I've heard similar sound while taking a high speed / high G corner. Heard the same rumble strip sound, and TCS light turned on. My assumption is the same - that's the diff making noise...

I think we may have found Jimmy Hoffa.

Check your trunk for a dead body.

Loose jack/nut

http://images.wikia.com/transformers...iledrivers.JPG

Personally, I'd notify Optimus Prime.

Just sayin...

I am having this EXACT same issue, it happens when I turn the wheel all the way (backing out of my driveway or making a U-turn)...

I am pretty concerned about this...

I have a BRZ manual FYI

DEFINITELY NOT that. This literally feels like youre driving over a rumble strip.

YES! AGREED! Same here

I started a thread on the BRZ forum to see if anyone on there is experiencing this as well...

(remove the spaces in the URL)

www . subaru brz forum . com/9-subaru-brz-general-discussion-forum/2828-issue-rumble-coming-rear-end.html

I had a truck that did the same thing, I thought it wad the transmission...