Do you have cell towers nearby? I have one within a mile and a half and had weird issues and found I needed an LTE filter on my antenna.
My immediate response to this is yes, because I have an app on my phone that supposedly shows what tower I’m pinging. I noticed months ago that when I’m home it was supposedly pinging a tower within a half mile or so of my house. I thought I even remembered spotting it on Google Earth. Now, at work, where the app isn’t pinpointing its location, I can’t for the life of me find it on Google Earth by just panning around where I thought it was, and every “cell tower locator” website I’ve tried isn’t showing any as close to me as I know this app was reporting. So the short answer is actually, “I don’t know. I’ll check it out again when I get home tonight.” But that’s a good thought if that gave you problems.
Some FM transmitters, if nearby, can also interfere. If that happens you need an FM trap.
FM Fool reports that the nearest transmitter is 12 miles from me.
Is your antenna outside and clear of most anything around it? Signal REFLECTIONS can do what you’re seeing as well. A nearby house on the backside of your antenna reflecting signal back to it (now out of phase) will give you multipath issues.
In my estimation, my antenna is clear of anything that I would think would be interfering with it. It’s mounted on the highest point of my roof with no obstructions in the immediate area.