Exhaust hanger 2000 SL1

I have a 2000 SL1 (130,000 km) on which I have just had the muffler hanger
changed with an OEM part. The heat shield was beaten up pretty bad so I
removed it from just forward of the muffler back.
When the car gets hot I get a nock from this area when the car is vibrating
(idle in reverse is the worst case).
I believe the problem lies in the hanger isolator on the body just above
the muffler. If I touch it while it is making the noise it stops.
My question is in regards to replacing this isolator. I would like to do it
myself but want to make sure that it is the source of the problem.
Has anybody else experienced this problem and how did you fix it.
Thanks