This walk-through needs a notebook, a clock, and a hand. Nothing here requires tools beyond what is already in the laundry room. The goal is a log that shows the change before anyone has to guess at it.
Set your baseline
Pick a load you run often, with the same fabric mix, the same moisture coming out of the washer, and the same setting. Note the cycle length and whether the load comes out dry at the end without a touch-up run. Repeat that load over several weeks of normal use so the baseline reflects your household and not a single day.
What to write down
Record the cycle length in minutes for the same load and setting. Note whether the moisture sensor ends the cycle sooner or later than your earlier notes show. Listen to the drum in the opening minutes and notice whether the sound changes as the load tumbles. Check whether the air at the exhaust outlet outside feels cooler than it did. Notice whether the room around the machine runs warmer than usual, and whether the cabinet warms unevenly.
Note any smell too. A faint warm smell during a new setting can be normal. A smell that shows up on every load is worth a line in the log, along with what you were drying and the setting you used.
How to read the log
A long cycle on a wet load proves little. Look for a steady drift across many loads. If the cycle has grown longer and the exhaust feels cooler under the same settings, the change is in heating or airflow, not in the laundry itself. Compare your notes with the clothes dryer page on this site, which gives the typical service life and when to plan. Keep your install year in front of you while you read it.
Check the simple things before you conclude anything. Confirm the lint screen is clear. Confirm the room has air coming in. Confirm the exhaust hose is not kinked or crushed behind the machine. Clearing lint and checking the hose are tasks you can do yourself. If these look right and the log still shows a steady drift, the next step is a look from someone who services dryers.
What to ask when you call
Bring the log, not a guess. Tell the technician the cycle length now and at the start of your notes, the settings you normally use, the change in sound, and any warm smell. Ask whether the pattern points to heating, airflow, or the moisture sensor. Ask what they will check first and how long the visit usually takes. Ask them to write down what they find, so the log can carry on from there.
Keep the log going
Keep the notes in the laundry room or in your appliance folder, and keep adding to them for as long as the machine runs. A long record makes the next decision easier, whether that is a repair, a planned replacement, or simply confirmation that the dryer still behaves as expected. Age is a planning input. The log turns age into something you can plan around.