Why is the roof leaking when it isn’t raining

All the advice so far about ice damns is valid. However, if there are no dams or visible water on the roof, then you will need to crawl up in the attic and start looking for the wet areas that are wicking into your ceiling. The insulation may have been soaked before you got a chance to clear the roof. Obviously if wet insulation is found, it must be removed. Another problem I have come across in a few situations like yours, no dam, but slow moisture stains keep developing, came from improperly installed "proper vent" from the soffit vents to the air space in the attic. In a few cases, the open upper end of the proper vent was blocked or covered with insulation and condensation formed on the top side of the drywall right along the wall. In a couple of cases, no venting was used from the soffit and insulation was packed into this area instead. In either case, you will have to get up there and move the insulation in the affected areas and look for the moisture. Also look for any tell-tale water stains on the rafters or trusses that may have been a leak from above.

Oh, wow. I'm sorry, but your roof is probably bad. If you can get the money you paid four years ago back (doubtful), I would, but you probably need to get that entire mess torn off all the way down to the decking, and probably quite a bit of the decking near the edges of the roof too. You can tell because the shingles look "lumpy" and have a rolling look to them -- like someone's melted them, especially near the edges -- and the valley is curved instead of sharp. I can also see the lines running across where different runs of roof sheathing panels meet (every 4' or so); that it's sagged in between these lines is a sign of sheathing damage.

Your roof isn't the shingles, so it doesn't matter that the shingles are only four years old. Your roof is actually the tar paper and ice and water shield that is underneath underneath the shingles. Multiple layers of shingles are bad; it means that they didn't replace the actual stuff that keeps the water out of your house, they just replaced the stuff that you see that goes over top.

If you go up into your attic when it's been raining quite a bit, see how much more of the underside of your roof sheathing is damp. If there's a lot, you need to get it torn off and replaced as soon as possible. If there isn't much, you have a few years to save up for it, but it looks bad now from the top. Make sure when they re-do it that they tear everything down to bare wood, remove all the nails and staples and junk, use Ice & Water Shield along the roof edges and in the valleys, and then put new 30 year tar paper and shingles over it. The tar paper and ice&water shield is what actually keeps the water out of your house. The shingles only protect the tar paper from abuse.