At idle or low RPM's, hot or cold, dead-stop or creeping forward, my '96 SL600 has developed a rapidly pulsing 'thump' sound on the right-hand side of the engine; not in the front of the engine, but on the right side. It is not metallic (as if a rod or valve train issue), but instead sounds pneumatic. The thumping sound has slowly been getting worse. Car performs wonderfully, but the thumping noise is now noticeable and... speaking frankly... is a little embarrassing. Could this be the RH side EGR Valve starting to fail?

__________________
MBCA Member #B012089 (Lone Star Section)
OBK Member #47 (W123 Division)
'96 SL600 (105K) Triple Black - Mein über-Fräulein
'79 240D (292K) Yellow/Saddle - Mein Spielzeug
'01 ML430 (123K) Black/Saddle - Wife's Ride
'94 SL500 (164K) Green/Champagne - Daughter's Dream
'73 450SL - RIP
'86 300E - RIP
'88 420SEL - SOLD
'94 S320 - SOLD