Pushing on the brake releases tension on the traction drive belt. So the first place to look will be the belt, idler near the engine, the idlers that swivel, spring, rear pulley, and fan. If the belt is cracked or has chunks missing, it can cause noise, but metallic sounds can be harder to locate.
I once had an LX188 wear the snap ring groove in the input shaft so badly the drive pulley was able to move down and began rubbing on the trans. case. I was able to see the shiny and sharp worn side of the sheave before removing the fender pan.
Hope you find something more simple. Can you describe the sound or about where it seems to be coming from?
Remove the mower deck and slide under there for a good look, engine not running, of course. I need to correct one part of the earlier post. There is no idler near the front on the LX176. So check carefully the idler assembly that is about in the middle of the tractor. That assembly pivots on plastic bushings that can wear out. You can take tension off the belt and idlers by locking the brake pedal down. The assembly should not be so loose on the pivot bushings to be rocked around much. Worn bushings will also cause the belt to wear from misalignment.
You may also be able to reach back to the tranny pulley to see if there is a problem there. That's about all I can think of until you get time to check those things.
Let us know what you find.
Had a similar problem on my old L108. Ended up being the bearings on the tensioner pulleys. They are sealed so they so you can't lube them & only last so long. Also replaced the drive belt while I was at it.
Found the rattle, it was, I guess what you call the drive belt guide. Broken in half, had it welded good to go. Looked like the belt had been rubbing against it..working fine now..
thanks for all the help everyone.
Sure mows pretty good, has the same feel as my Kubota T1670. I think the JD may be a tiny bit faster but isn't as nimble as the kubota. Both are old but in good shape, I feel like I got a good deal on the JD for 400.00. Now no more loading up my kubota or badboy to mow where my wife has horses.