You probably damaged one of the heads when you dropped it and this is likely the reason for the noise. Assuming that your shaver is like the one pictured here, remove the head by pulling it straight up and off of the shaver as seen below.
Then tun on the shaver. If is is quiet without the heads on then you can assume the heads are the problem and should replace them. You will find replacements at shaveroutlet.com. Heads for the shaver picture you selected are linked below
Answers & Comments
You probably damaged one of the heads when you dropped it and this is likely the reason for the noise. Assuming that your shaver is like the one pictured here, remove the head by pulling it straight up and off of the shaver as seen below.
Then tun on the shaver. If is is quiet without the heads on then you can assume the heads are the problem and should replace them. You will find replacements at shaveroutlet.com. Heads for the shaver picture you selected are linked below
http://shaveroutlet.com/norelco-philips-hs85-replacement-heads-p-253.html