How can I find out what's burrowing under my carpet pad?

Pest control should set some live traps. They also should be able to determine or find what it is. Could be a mole, chipmunk etc.

Get a new pest control company, the one you have isn't doing the job.

After you catch the critter, consider ripping out the old and installing new carpet, because the critter has surely left waste all over the place under your carpets.

If it were me, I would pull the carpet back and find out. The area needs to be sanitized. And get whatever it is out! Anyone you know that will loan out their cat or dog for a few days?

Thanks for your help. I'm installing hardwood floors so everything is going.

My friend works for a company that is engaged in the extermination of insects and he usually helps me every season.

You should switch to a different company is this is the case

Calling a professional is always a good option since there are many things that can hide there. When I've bought the house that I'm staying in now, I've started to notice some noises coming from the basement. I've decided to investigate and to my surprise, there were some miles there. Immediately, I've grabbed my house and a professional that deals with mice control service and the problem was solved eventually. Now, I can use the basement in peace, without having to worry about anything. Mouses are freaking me out, to be honest, and I can't stand seeing them haha