I just recently within the past week got mine. When it's in the Jeep, and bolted up to the external antenna, it sounds like the traffic is in the passenger seat. However, when it's sitting on the desk charging all night, I found a similar problem to yours with my state's Highway Patrol. My home is practically a Faraday cage, and I experience similar issues with other radios, and even cell phone reception.
Tried a few different rubber ducks, and eventually found a place on the desk by moving it around where it receives nicely. Troubleshot it with a Pro-106, and the HP was just as strong.
I also use the Butel software with the HP, as I do with all my radios. Anytime I encounter a problem, I find it easier to backtrack and correct errors.
One more note, when you program a system with this thing, make sure you're selecting EXACTLY what you want. In my state, if you select what you want to monitor, you can easily program an entire state's worth of repeater systems to monitor 2-3 agencies, and it takes forever to scan.
Little more information, luckyshrew13. Is this a new HP-1? Have you had the system programmed and were able to hear it or have you just programmed it? HOW did you program it? Are you going off of the full database or did you program it as a favorites list? Did you download the latest firmware and database to Sentinel? Did you then write to the scanner?