Sump pump runs every 1 1/2 minutes.

For the last week or so, we have noticed that our sump pump runs for about 10 seconds every minute and a half or so. The pump is sealed in the pit due to a radon mitigation system so there is no way I can see what is going on without cutting PVC piping or breaking the seal, which I don’t want to do if it can be avoided. We have had rain recently but I fear this is more than just normal operation. I can hear water trickling loudly when the pump is not running and I can hear it gushing when it is running. My guess is that the check valve is malfunctioning, but I don’t know how to troubleshoot it. And help would be much appreciated. Thank you.