I've found that older quads were always RF noisy on their own. Some LED systems are really noisy. Carrying a VHF on me while riding usually resulted in some sort of hash just from the ignition system.
But sounds more like something changed when the antenna was damaged.
I'd probably check for continuity from end to end on the coaxial cable on the shield and center conductor just in case the mount was damaged. And while the antenna will work without a ground plane, it still needs a ground. Make sure your radio is well grounded and so is the antenna base. Also, try moving the antenna around and see if you can find a quiet spot.
As for antennas on quad/UTV's, I'm using Laird half wave VHF antennas on ours. With the spring in the base, I've hit tree branches at 30+ MPH and not had any issues. In fact, the one I have on my Polaris Ranger has a permanent kink at the tip of the antenna from getting hit. Been on there for about 5-6 years with probably a few thousand miles on it. I discovered a long time ago that the ham/hobby grade antennas are not very durable. Give one of these a try next time:
https://www.theantennafarm.com/catalog/laird-technologies-b1442ns-7116