There are only two ways a dryer dries clothes: it makes heat, and it moves air. When drying time doubles, one of those two has stopped working properly, and telling them apart takes about a minute.
Put your hand near the outside vent while the dryer runs on a heat setting. Strong warm air means the heating side is fine and you have an airflow problem. Weak or cold air at the vent, with the drum still turning, points to the heat side: a heating element, thermal fuse, or thermostat on an electric dryer, or an igniter, coil, or gas valve on a gas one.
Airflow is the more common of the two, and in older Bronx, Brooklyn, and Queens buildings it's the more urgent. A vent run that travels twenty feet through a wall, sags between joists, or ends in a flap crusted shut with lint will choke a dryer slowly over years. You'll notice the drying time first. The fire risk is the part nobody notices.
There's a trap here worth knowing about. A blocked vent makes a dryer overheat, and overheating is exactly what burns out thermal fuses and heating elements. Plenty of people replace the element, get two good months, and watch it fail again — because the real cause was never the element. Any honest dryer repair checks the vent as part of the same visit.
If the drum is squealing or rumbling on top of everything else, that's separate: rollers, a belt, or an idler pulley. Worth fixing, and usually inexpensive, but it won't change your drying time at all.