Vibration??
Arg. Sounds like a rod knock. :(
Took it out on 295 & opened it up to about 70. Sounded like someone was jackhammering under the hood. When I parked it in the driveway, heard a nice knock at idle. Sounds like a rod knock...although there's no vibration at speed, and the knock quieted down after a bit.
Does sound like something's not right in the bottom end.
Great. :sigh:
(edit): confirmed. #5 has bitten the dust. Hasn't windowed the block yet, but it's just a matter of time...