I have an 18' above ground pool with a hayward pump and cartridge filter. Last week I removed the pressure gauge and put a new one in. Just before I did that, the filter or pump started thumping and vibrating loudly. I had a lot of pressure and suction. When I held my hand over the return into the pool the noise stopped. I thought maybe it was the pressure gauge because it was bad, but it hadn't caused me any problems. I replaced the gauge but it's still doing it. It actually sounds like the filter is going to blow. It keeps getting louder. I've only had it 2 years. The cartridge has been cleaned and I cannot find any type of blockage. Water is getting dirty! help!!