Here's what the UH1H Pilot's Operator's Manual aka "dash 10" says:
8-46.
Collective Bounce
Collective bounce is a pilot Induced vertical oscillation of the collective control system when an absolute friction (either pilot applied or control rigged) is less than seven pounds. It may be encountered in any flight condition by a rapid buildup of vertical bounce at approximately three cycles per second. The severity of the oscillation is such that effective control of the helicopter may become difficult to maintain. The pilot should apply and maintain adequate collective friction In all flight conditions.
9-28. Collective Bounce
If collective bounce occurs.
1. Relax pressure on collective. (Do not ’stiff arm’ the collective.)
2. Make a significant collective application either up or down.
3. Increase collective friction.