Noise from Cam Sensor

I read the other info for this subject, i also had the tensioner belt, pulley replaced. My question is, since i still get the squeaky noise (not as much) did i need to pay to get the tensioner changed out? The dealer is now telling me i need the cam sendor changed out. The dealer says yes - why? if i still get the noise, did they misdiagnose the first time?? Thanks for any info.