Funny you mention air pockets—I chased a knocking noise for days too, convinced it was trapped air. Bled the pipes twice, no luck. Turned out a sneaky section of pipe was expanding against a joist every time hot water ran through it. Little shim and some padding fixed it right up. Sometimes pipes just wanna keep you guessing... Glad yours was simpler though, bleeding air is way less hassle than crawling around with insulation in your hair, trust me.
"Sometimes pipes just wanna keep you guessing..."
Haha, ain't that the truth. Had a similar one last winter—spent hours convinced it was air bubbles, but nope. Turned out the pipe hangers had loosened up just enough to let the pipes dance around when the heat kicked in. Tightened them up, added a bit of padding, and silence ever since. Plumbing's funny like that...always something simple disguised as a mystery. Glad you sorted yours without too much attic yoga.
Had something similar happen in one of my properties. Thought it was the hangers too, but turned out the pipes were resting against a wooden beam—so every time the heat kicked on, they'd expand and start creaking like an old ship. Ever check if yours were touching any wood or drywall? A bit of foam insulation between pipe and beam solved mine pretty quick. Plumbing mysteries never fail to surprise me...
Had a similar issue myself, and you're right—pipes expanding against wood can really amplify noise. Foam insulation is definitely effective, but I've also found that using recycled rubber strips between pipes and beams can offer a durable, eco-friendly alternative. It dampens vibrations nicely and holds up well over time. Plumbing quirks like these always remind me how small adjustments can make a big difference in home comfort...
"Foam insulation is definitely effective, but I've also found that using recycled rubber strips between pipes and beams can offer a durable, eco-friendly alternative."
Good call on the recycled rubber strips. I've used them a few times myself, especially in older homes where the pipes have settled into awkward positions. One job comes to mind—a client had this persistent ticking noise every time the hot water kicked in. Foam insulation helped a bit, but didn't fully solve it. Eventually, I tried sandwiching thin rubber strips between the pipe hangers and joists, and it made a noticeable difference. The rubber absorbed vibrations better than foam alone, and it held up nicely over time without degrading.
One thing I'd add from experience: make sure not to overtighten the clamps or hangers when installing the rubber strips. Leaving just a tiny bit of wiggle room allows for natural expansion without stressing the pipes or fittings. Learned that one the hard way after having to redo a section that started leaking from too much tension... plumbing always finds a way to teach you something new.
