Oil pressure/filter

[LasVegas]

Interesting phenomenon. Had the oil/filter changed about 3 weeks ago. Using Mobile synthetic. After the oil change I noticed the oil pressure going as low as 20 lbs at idle after warmup. Other days it would stay around 30. At speed normal at a little above 40 lbs. I went back to them and asked them to change the oil filter and they assured me the oil change had nothing to do with it. Today I was sitting at a stop light at 20 lbs. B.S. Went back and told them to change the filter. They again said it had nothing to do with it but they would change it. They did and now the pressure is as its always been...around 35 lbs at idle. Obviously something strange in the oil filter. Just a heads up if anybody has this happen.