Sounds like one or more possibilities.
Could be sweeping too fast.
Could be SENS set too high.
Could be that you're catching just the edge or corner of a piece of iron.
Could be multiple target metals under the coil at the same time.
I suggest slowing down first. You might try actually seeing just how slow you can go and still get a response. It's not that the machine reset speed is slow, but if there are multiple objects being detected going slow helps to separate and lock an ID. If you're just catching the edge or corner of a junk object, slowing down will allow you to recognize that the target isn't where or what you think it is. And IDs that jump around too much won't be coins. If it jumps more than one ID notch in either direction it's likely junk.
If that doesn't help, or doesn't help enough, turn down the SENS a bit. You won't lose much in the way of depth until you're down under 18 or so.
Don't chase chirps! Until you learn what coins sound like you'll just frustrate yourself unnecessarily. Focus on signals that are solid even when you turn 90°. And pinpoint the same way.....locate from two different positions around the target. Do not worry about what the ID says in pinpoint unless it gives negative values every time over a target.
You didn't say which coil you're using, but a DD and/or a smaller coil might be in order, especially if trash density is high.
I just got a new digital video camera, and I'm planning to start making some videos that will address some of what I'm describing in the not too distant future.
