Rattle & buzz, 46rh

My 95 3/4T pickup with a 360, noticed a rattle in all gears at 1500-2000 RPM yesterday. I'm guessing at this 'cause I don't have a tach. Worst when accelerating from low speed/stop, almost like detonation. Today when I was running the truck through it's gears in the driveway it starts to buzz in reverse, but no other gears. I can make it much more pronounced by "powerbraking" in reverse, then throttling up from idle. Into the shop, drain the trans (ATF-4,15 months/15k old,looked a little darker than I'd like), nothing in the pan or filter. Spotless,almost. Both bands still right on for adjustment, shift linkage and throttle pressure adjusted correctly, flex plate bolts tight, no dust shield contact. Any ideas before I dig deeper? Oh yeah, did I fail to mention it's got 229k and never been touched...

I've heard torque converters make noise when they start to go south. Make sure it's not something simple like cat. converter internals or exhaust heat shields buzzing/rattling. Just a thought.

Yep, I'm a little concerned about the torque converter, I've heard/read the factory ones leave a bit to be desired. Good point about the cat, but mine's an empty shell. I rodded it out after it clogged a couple years ago. I need to climb under the truck in the morning and shake the tar out of everything to find the rattle, but as for the buzz?

if it does it while power braking, get a vehicle operator to do that while you lay on ground NEXT to the vehicle and try to look up under it to ID the source.

do NOT lay where the vehicle may drive if something goes wrong--if it's in reverse, stay on the sides or in the front, and out of the way of the tires!

I'm wondering if the flex plate is broken or if bolt/s are loose.

I pulled the dust shield and checked the flex plate to converter bolts, good and tight. From the motor side the flex plate looks fine, don't see any cracks,etc. I wanted to drain the converter, too, but evidently this one doesn't have a plug. Found a few other sites that refer to the buzz in reverse issue (even a TSB to go with it), doesn't sound like I should worry too much. The two noises probably aren't even related. At this point I think I'm gonna filter & fluid it and let 'er roll. Funny thing is I bought a torque converter and a complete kit for this trans 5 years ago, still sitting on the shelf. Sometimes my luck and my common sense don't travel down the same path...