Unfortunately, the windows probably should have been addressed before the new siding went on. Doing the windows before putting on new siding would have given you the option of using new construction vinyl double hung with J-channel build into the frames. It also would make repairing or replacing rotted framing members much easier.
However, since you already have the new siding up (would like to see a pic of the window with the new siding in place) you may have to use replacement type windows. If you have rotted frames, those will have to be replaced and the new replacement windows sized to the opening AFTER the frame is fixed. Of course you can carefully calculate the opening based on what you intend to use to reframe the opening, but that can be risky for an amateur. Keep in mind, replacement windows usually have to be ordered to you exact size and are not returnable if you measure them wrong. Always a good move to have supplier measure and order the windows for you. After you install the new replacement windows, you may have to install some new extension jams and exterior trim in order to fit snugly to the new siding. Don't forget to use Ice & Water shield under the finish frame/ over rough opening framing and caulk all areas where water could possibly get in.
Soundproofing as it relates to windows is all about mass -- the denser the materials, the more sound reduction you'll get. PVC is, indeed, typically more dense than the far more lightweight aluminium and so will will resist noise transfer more. However, the amount of surface area made up by the frame is absolutely dwarfed by the glass itself. Any differences in the frame will be massively overshadowed by the properties of the glass, make it a moot point.
PVC/Vinyl windows do a far better job of restricting conductive heat as they are a much better insulator than aluminium. Aluminium is really one of the worst materials to use from an insulation standpoint.
However, PVC/Vinyl will eventually "melt" in a hot environment. Recycled PVC will do so far faster than virgin PVC, but even the latter will eventually sag enough that opening and closing the window will be tricky. Assume maybe 15-20 years.
Aluminium will last indefinitely. That and the price are typically the two big selling points of that material.
In short, neither has a true advantage from a soundproofing perspective (the glass does quite a bit, though) but PVC is a better choice from an insulation standpoint if you are willing to replace the window every 15 years or so. If you don't care about the insulation value and don't want to replace the window, then aluminium is the way to go.
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Only guessing, but many cleaning agents are made up of chemicals (bases) that tend to be slick which helps in most cleaning situations. Perhaps clean the inside of the track with acetone or brake parts cleaner to remove any of the former cleaning residue. Perhaps that will restore the friction needed to hold the awning open.