Do you take your Toprol at night or in the a.m.? Taking it at night, about an hour or two before bed, might really help with the sensation...have you asked your doc about increasing your dosage? I was on 25 mg of atenolol and found that 50 mg was much more relieving. I know about the horrible pounding heart feeling, it's incredibly annoying. I found out mine was caused by hyperthyroidism so that's why I asked!
You might find that exercising 15-20 minutes, getting your heart rate up to 70-80% of your max (although in your case you might want to go slightly lower because you're on the beta-blocker), might drastically improve your symptoms for several hours afterwards. I've always found that helps a lot. I've been on the atenolol for about a month now and find that my heart rate is significantly lower when exercising than it used to be; but it's still okay to exercise on it as long as your blood pressure stays within the normal range.
I know how uncomfortable this is, hang in there!