Unfortunately, the cracking/ popping noises are normal for baseboard
Luckily, there's an easy fix to eliminate the sound or at least make it less noticeable. The noise is essentially caused by the heating element being installed on a wall that is warped or slightly uneven. To fix it, just readjust a few screws so the unit fits snugly against the wall without pinching the element.
The paint cracks because of differential expansion and contraction rates. The quarter round and the baseboard expand differently and that movement causes the paint to crack. Cheap, fast dry, painters caulk tends to dry pretty hard. As such, it also has limited ability to stretch or flex.
Expansion & Contraction
All the temperature change in a hydronic baseboard heat system causes expansion and contraction of the materials, especially metal, around the pipe. Sometimes this causes noises. Some quiet clicking is expected and isn't a cause for worry.
If what you are hearing in your baseboard heating system on the second floor is a "gurgling" sort of sound, then I would suspect that what you are hearing is being caused by air trapped in your system. Not only does this cause an annoying sound, but also it will prevent your second floor from heating up efficiently.
Caulk around frames for exterior doors and around trim and baseboards where they meet the wall and floor with an interior-grade caulk. Use a clear-drying caulk for hardwood or tile floors and trim with natural wood finishes – and paintable caulk for painted trim and carpeted floors.
The most common cause of airbound pipes is a leak somewhere along the way. The water flowing through the pipes is so hot that even the smallest hole or leak can cause small amounts to evaporate. As the water evaporates through the hole, it's replaced with air.
However, if you hear rushing water either in the baseboard or the walls around the baseboard, there may be a problem. Over time, units can lose water which in turn allows air in. That rushing sound means that it is time to have your heating serviced.
Shut the valve nearer the boiler and use the pump to force water from a bucket into the hot side and let it come out the cold side back into the bucket until the bubbles stop. Again you can go around and open and shut the various radiators to force water through every loop.
Caulking is required if there is a gap of at least one-eighth of an inch between the flooring and the baseboard.
Quality wood baseboards can last decades when properly maintained.
If you plan to install baseboard moulding before adding carpet, it needs to be installed 1 inch above floor level to allow room for both pad and carpet. If adding baseboards after carpet is laid, it should be installed at the same height as without carpet.
For engineered wood or solid wood flooring, floorboards can often squeak because they are rubbing against each other. Powdered graphite –the same as what your pencils are made from! – is a great fix for squeaky floors. It works by reducing the friction between wood and it's also easy to apply.
Use the hammer to attach the baseboard molding.
Use a wall stud finder to work most effectively. You may also perform a knock test on the wall to identify the empty spaces between the studs. Insert two finishing nails into each stud at the base of the baseboard. Using a nail set, hammer the nails in at a steep angle.
Vacuum baseboards using the brush attachment, then detail any grooves with a soft-bristled brush. Fill your bucket with warm water and add a cup of distilled white vinegar. Use a microfiber cloth to clean the baseboards, rinse the cloth frequently, and dry the baseboards immediately after washing.
When pipes leak, water can seep behind your walls for days unnoticed until mold rears its ugly head. Signs of baseboard water damage include peeling paint, visible stains, or the baseboard physically breaking apart from the wall.
Persistent sounds of water running when no fixtures are on could be indicative of a water leak. Leaks can occur in pipes, faucets, or within the walls, leading to water wastage and potential damage. If you suspect a leak, it's advisable to seek professional plumbing assistance to identify and address the issue.
Unusual Baseboard Heater Sounds
Bubbling and gurgling sounds in the system are often associated with air in the lines, which if this turns out to be the case, can often be resolved by an experienced service technician or plumber.
If you have multiple baseboard heaters on the same circuit and one of them stops working, that's a sign the thermostat has malfunctioned.
This means that behind your trim there is nothing but empty space which makes a great place for drafts to start. How to fix this? Use caulk to seal joints in the boards and gaps between the trim and plaster.
If your baseboard heater has a built-in thermostat, you can adjust the temperature by rotating the knob. Turn the knob counterclockwise to decrease the temperature and clockwise to increase it.
The gist is that cold air from the window mixes with warm air rising out of the baseboard, that warm air moves around the room, cools and sinks back to the floor, where it is eventually re-heated by the baseboards. That's why traditionally it's recommended to install a baseboard under a window.