That's what I got too the sonoline B 3mhz. It is the best thing I bought and really not that expensive. Davies, I listened to some on You Tube and listened to yours while I was trying to figure out how to use mine. This was when the batteries weren't working. I could turn it on but couldn't hear anything. Anyway, yours sounds exactly like the others. It's the hb. It's not anything else. Your scan is going to be brilliant tomorrow. And I agree a medium bladder is better than a super full one.
This is the best invention! Though I did have a bit of a panic when I couldn't find it again last night. But I'm going to try to relax and remind myself that they can move and hide.