Gear box rattle

[bobg56]

It started a while ago and got progressively worse so at 590 hrs. (and little to no use of 100LL) I sent it off to Lockwood Aviation for the 600 hr inspection. After re installing it the rattle was not better but worse. At 610 hrs. I then sent the carbs to Lockwood for the 200 hr and 5 year rubber replacement. After installing them and doing the carb sync using the electronic Carb Mate, balancing the prop using a Dyna Vibe to .03 IPS I still have the rattle, accelerating from 2000 rpm to 3500 its pretty noticeable, however when the engine is cold (first start) using choke there is little to no rattle until the choke is removed then rattle starts. Once engine doesn't need the choke re applying it causes engine roughness. It's hard for me to wrap my mind around how the carbs can cause gear box rattle. The carbs are perfectly synced, I'm very experienced at doing it. For T/S purposes I have removed the pitot probe, the oil dipstick, removed engine cowls. I've been in contact with Lockwood and I'm getting ready to send the gearbox back. I had already pulled the magnetic plug, did a friction check test, 45 ft lb. One unusual thing, after the first flight after GB re install I noticed a squelling noise if you turned the prop backward, (I needed to access cowling screws so I turned just a few inches) I called Lockwood about this and was told the noise will go away after 10-15 hours and it did. I'd like to know if anyone else has had something like this occur and what was the fix...thanks