So your car makes noise when the car is accelating.
Well, it could be some drive train parts and/or engine.
Possibly parts are
1. bearing
2. flex disc
3. engine mount
4. transmission mount
5. distributor/rotor (misfiring)
etc....

Since I changed pretty much everything and also did some special work on my SL.
I changed
1. Major engine electronically parts (plug, wire, rotor, cap, coil, DS, alternator, and etc.)
2. Major mounts and suspension parts (engine, transmission, def, subframe mounts and all suspension bushings with Bilstein shocks as well as bearings)
3. exhaust parts (ANSA muffler, sports catalytic converter)
4. interior parts (all wood panels, dash cover, wood knob, and all chrome parts)
5. inject hard Urethane form to the both side sills (giving 2 solid fat bone to the floor)
See this HP.
http://www.sun-inet.or.jp/~bellco/essh.htm
Also custom made front brace.
Since I have AMG 17inch wheels on my car, I should have stiffer body even it is convertible. So I came up to all these modifications.
With all of them, I think I have pretty flat ride even better than original body.

About engine, it makes much better gas mileage with MDS and power coil. I had about 4km/1L when I bought, but it is now 6km/1L or better.
They even makes better idle/accelation so I think they worth to pay $150.00

Ezzy.