Don't think it will be noise and I wouldn't mess with de-bounce has it will just add a delay to the homing process and make it less accurate.

More than likely you have Dodgy switch or lose wire connection, possibly bit of crap in the switch if Micro type.?

Did you try restarting PC and trying again.? Could have possibly been a Mach issue i've seen it do daft stuff like this before and be fine after restart.!