On both German and American GTI forums it's a very well known issue, mates.
The H&R Mono has too much travel (at bump), so that the drive shaft touches the frame.
This is the case on track and sometimes even on street.
H&R Mono:FK:Remember the right-hand (driver side in the UK) driveshaft is longer than the left-hand:
Not an issue with most coilovers. Many H&R owners reported this, some KW V1-V3 and
FK owners, but as far as I know no AST, VWR, Sachs and Bilstein owners.