I was called in to look into noise complaints in a large law library. A Trane heat pump above the ceiling in the stacks was making horrible rattling noises. Most of it was caused by tubing banging into adjacent tubing and devices within the unit. Several of the tubes had noticeable divots in the copper - including one in the hot gas line. It wouldn't have been long before that unit was oil-drenched inside.
I've never seen any other WSHP units that have so many problems with this.