Strange rear of the car low frequency rumble when letting up on the gas

[Pat Martone]

I’m at a loss in discovering the source of a low frequency rumbling sound coming from the rear of my ‘31 Slant sedan, when I let up on the gas pedal. This is not an engine or exhaust noise. I have checked/adjusted the tailpipe muffler clamp several times, so I don’t think that is the source. I’ve even wrapped a piece of high temp silicone rubber under the tailpipe clamp to isolate any tailpipe vibration from being transmitted to the frame. I welcome any thoughts on the cause of this annoying and prominent sound. Thank you.

[Step-down]

My issue sounded like yours , I replaced u joint and front bearing in torque tube

[WHN]

I would look towards the u-joint also.

Two quick things that I would do. Check your transmissions oil level. Than using John Deere Cornhead grease fill your u-joint cavity until it starts coming out of speedometer gear opening. Could take a full tube.

I have seen U-joints that have been bone dry for years. Enjoy.

[Tom Wesenberg]

If the U joint is OK, then I'd check the differential pinion nuts and bearings.

[DHZIEMAN]

Originally Posted by Pat Martone

I’m at a loss in discovering the source of a low frequency rumbling sound coming from the rear of my ‘31 Slant sedan, when I let up on the gas pedal. This is not an engine or exhaust noise. I have checked/adjusted the tailpipe muffler clamp several times, so I don’t think that is the source. I’ve even wrapped a piece of high temp silicone rubber under the tailpipe clamp to isolate any tailpipe vibration from being transmitted to the frame. I welcome any thoughts on the cause of this annoying and prominent sound. Thank you.

Check U joints! Sounds like a U joint issue!

[Pat Martone]

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Thank you for the informative replies.
I wonder if this additional info below would impact your previous replies about potential U-joint or differential/pinion issues:
My car makes these low frequency rumbling noises, coming from the rear of the car, when the transmission is also in neutral and the car is stationary; I hear it when I rev the engine and remove my foot from the gas. Thanks again.

[Big hammer]

With my 31 Tudor the rear seat cushion is removable and a great space to store stuff ! I would have to be careful what I stored there. Also maybe the body mount bolts might be a little loose.

[Pat Martone]

Thanks, Big hammer.
I checked out your suggestions, but so far, no luck finding the smoking gun.
I welcome any other suggestions. Thanks again.