Originally Posted by LexxLovesMusic
the particular scanner I am using when this happens is a Radio Shack pro 2051. I am usually in the 144.xx to 146.xx range.
Most likely intermod from a mix of two transmitters or a direct image from a paging site in the 152 or 158 MHz paging bands.
Setup a search from 152 to 153 MHz and 158 to 159 MHz and see if you hear the same type sounds.
The correct way to cure this is the use of a notch filter tuned for the true paging frequency. You can monitor the paging bands and find the true frequency using a 2nd scanner searching the paging bands and just match the sounds you hear. PAR Electronics sells them. One for each of the two bands. They work fantastic for these problems. The NOAA WX transmitters also caused this problem so they sell notch filters for that also.
Most of these problems were cured when they started selling better quality scanners using triple conversion IF circuits. The older dual conversion models were very prone to this problem. I'm not sure if the 2051 is dual or triple conversion.
Using PL or DPL squelch may keep the scanner from opening the squelch but if the ham repeater you are monitoring does not transmit a PL or DPL code, then that won't work. Also the paging noise will usually still come through when the scanner is receiving a signal with the proper tone squelch set and the paging transmitter comes on. If the intended signal is much stronger then the paging interference, using tone squelch may help as the real signal will mask the weaker paging signal.
If the intended signal is weaker than the paging signal, then you are SOL without some type of notch filter for the unwanted signal.
Edit: what W8RMH said is also a very possible cause. Packet radio or some other digital mode. All you can do for that is set your search around the noise or see if you can lockout individual frequencies while searching.
My bet is still intermod or an image from a VHF paging site. It is a VERY common problem with scanners.