Car just started making a very audible low-pitched rattle/grinding noise when backing out of the garage on very cold (Florida) days, basically anything under 50 degrees. Driveway is about 100' in Reverse with noise, then shift into Drive on the street and no more noise after driving about 50 more feet. The car won't make the noise in reverse when its warmed up and makes more sound the colder the air is. My mechanic can get me in sometime in the next couple of days, just wanted to try see if I could solve the mystery to help him diagnose the issue.

I'm guessing motor or transmission mounts, or the exhaust is bumping into something. Car is stock except resonator/secondary cat delete with about 70k on the clock.

 

The diff death rattle?

 

Thanks Finny.

I'm having a hard time interpreting the response. Is that just a guess or likely the issue.

 

Put your foot firmly on the brake and shift from D to R to D to R... do you hear a clunking sound or some play? If so the centre could be chewing it self out.

The sound may go away when the airmatic corrects itself as you may be losing hight overnight. Something rubbing when the car is lower.

Other possibilities include the heat shields rubbing on the tail shaft or something rubbing on the axles.

Get it on a car lift and have a look under there... could also be foreign road matter etc...

My 2 cents....

 

Thanks again Finny. Ended up that a transmission mount cracked, which lowered the exhaust pipe enough that it was rattling on a cross brace.