Hi guys,

Been chasing this one down since I bought my 4.5 a few weeks ago.

It started out only at idle in drive. Reverse, neutral, park, no noise. To me it first sounded like water boiling in a pot, from right in front of the driver.

Professor at my auto class listened to it and said it sounds like something hitting. I've started to come over to that line of thinking.

At speed or heavy acceleration, can't hear it at all, but now I notice it under light acceleration as well.

Again as soon as you shift out of drive it disappears.

Thoughts?

If it's under load, I am going to guess that it might be engine mount or trans. mount. Have you tried looking/listening at your engine while someone is in the car and places the car in drive (left foot firmly planted on brake of course)?
See if your engine moves excessively when D is engaged and mild acceleration is applied.
Chasing vibrations, sounds and smells can be frustrating but none of those things are good in a car.
Best of luck

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1976 280C
SLOWER DRIVERS KEEP TO THE RIGHT.
DRIVE RIGHT PASS LEFT

PO says he replaced them and had receipts. I will have to check them all out again.

I did have the professor pop it into drive while I listened, but I could not hear anything abnormal from outside.

I checked engine and trans mount and both are good and new. The little engine shock needs new bushings but I'm not sure if that would cause a rattle.

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1973 280SE 4.5

I can't remember if the 108 had any heat shields on the mufflers or not. I had one of these work loose and it gave me the same rattle.

Of course it could be anything but this is easy to check. All it took was adding one self-tapping screw to bolt the thing down tighter.

If a heat shield is there then remember: These will flex since they are not made of case iron, just a thin sheet of stainless. But they should not wobble and be firmly attached to the car.

My W108 was also making that noise on acceleration. Do you have the floor shift or column? Mine is floor shift and it was a worn shift linkage bushing which allowed the linkage to wander over under acceleration and rub on the flex disk. Sounds just like rocks in a metal pan.

Mines a floor shift auto. The sound/feeling is more firewall/front of driver than trans area though.

Think I found it. Zero bushing in my control rod linkage. So it's just flopping. Ordering bushing will report back if it helps.

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1973 280SE 4.5

Replaced the dead bushing but no luck still have the noise only in drive. I can get it to do it steadily with a particular amount of throttle while sitting with the brake applied.

I think the noise may be trans area. These vids are with my phone in the footwell.

Sitting with the brake on and giving it steady throttle to get a stable noise: 20180330 230015 - Sendvid

Normal driving, you can hear it at the beginning and end of the vid: https://sendvid.com/ykldnj33

Replaced a shift linkage bushing that was totally gone but that wasn't it.

Interestingly I could not get it to make the noise on the off with the wheels off the ground. However 2 weeks ago it would. Not sure what would explain the discrepancy.

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1973 280SE 4.5

New video of the noise this morning at a stoplight.

http://sendvid.com/zlonambm

Sound familiar to anyone?

Update: it was exhaust pipe touching trans cross member. Stuffed a few rubber donuts in the mid-body mount point to create some space and it worked.

Couldn't see it on the lift as the exhaust would sag away.

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1973 280SE 4.5