The short answer
A thump with a rhythm tied to the drum means something is either on the drum or riding round with the load, and that is a much shorter list than a general noise. On a Bosch dryer it usually means a worn drum support or a tired idler pulley rather than the motor — these are the parts that carry the drum and they wear predictably. You can locate the noise and rule out the free causes in minutes; replacing what it points at is generally service work.
What you observe
- A heavy thumping, once per drum revolution — Something is either on the drum or being carried round by it, and the rhythm is the giveaway.
- A vibration you feel through the floor — More a shake than a sound, often worse on a suspended or uneven floor.
- A rattle or a clatter that comes and goes — Coins, buttons or a bra wire loose in the drum or caught in the blower all sound like a serious fault and are not.
- NEAR MISS — the noise came with the drum stopping — A noise followed by no rotation is a belt that has broken; that is a will-not-start page.
Causes, most likely first on Bosch
- Worn drum glides, felt or rear bearing — The drum rides on low-friction pads at the front and a bearing or roller arrangement at the back. Ranked first on Bosch: it is the part that carries the load every single revolution, so it wears first on almost every dryer platform, and the noise it makes is unmistakable once you know it.
- A restriction in a path built with very little margin — Filters, small-bore hoses and close-fitting seals are what make this class of machine quiet and efficient. Second on Bosch because the narrow-tolerance paths are the first thing to foul on this construction, and clearing one costs nothing but time.
- Support rollers flat-spotted or seized — Many platforms carry the drum on rollers. Third on Bosch because it is the other half of the drum-support story and it shares the top of the list with the glides, differing only in the sound it makes.
- A failing drive motor — A motor bearing going down hums, growls or screeches and does it at motor speed regardless of what the drum is doing. Last, and that is the whole point of the order on Bosch: it is the least likely source and the most expensive, which is exactly why it sits at the bottom of the order and not at the front of your mind.
- Body: Bosch builds for quiet, which means tight clearances and fine filtration throughout — and those are the first things to foul, long before anything wears out. The ranking below follows that construction.
Check in this order, and why
- Check what tight-tolerance build means for this machine — First, because it splits the top of the ranking from the rest. Find and clear every filter and screen the machine gives you access to before touching anything else.
- Turn the drum by hand with the power off — Second, once that is clean. Roughness, a catch or a gritty feel as it turns tells you the support is worn before you take a single panel off.
- Reach right round inside the drum and into the lint duct — Third, and only if the two above told you nothing. Coins, buttons and wires collect at the front lip and behind the filter housing, and finding one ends the job.
What an owner can safely check
- Empty the drum and check every corner of it by hand — Run a hand all the way round the drum lip and the seal, and look into the lint filter housing with a torch for anything that has escaped a pocket.
Tools: torchAbout 10 min
- Level the machine at all four feet — Adjust until the cabinet sits solid with no rock at any corner.
Tools: adjustable wrench, spirit levelAbout 20 min
- STOP HERE — the remaining checks are on live terminals — Nothing beyond this point is worth doing yourself, and nothing beyond it is cheaper for having been attempted first.
Before you open anything
Safety
Unplug the dryer or switch off its breaker before you open the cabinet — a dryer circuit is a high-current circuit and the element terminals stay live at the block until it is off. On a gas dryer, shut the gas valve at the appliance as well, and if you smell gas: do not switch anything on or off, leave the building, and call the gas utility or emergency services from outside.
When to call a technician
Call when the noise tracks the drum, survives an empty air-only run and the machine is level — that is a support or belt component behind the cabinet and it needs the machine opened.
Nearest pages of this class
What this page does not cover
This is generalized information for Bosch dryers as a class, not for one product line or one model. Where a line-specific page exists for this brand and appliance it is linked below, and it is the more specific answer — start there if your unit is one of those lines. What is deliberately absent: part numbers, torque figures, wiring colours and panel-removal sequences — every one of them varies by family and belongs on the page for that family.
Links: - [Bosch T Dryer: Abnormal Noise or Vibration](/blog/bosch-bosch-dryer-t-dryer-abnormal-noise) - [Bosch WNA Dryer: Abnormal Noise or Vibration](/blog/bosch-bosch-dryer-wna-dryer-abnormal-noise) - [Bosch WPA Dryer: Abnormal Noise or Vibration](/blog/bosch-bosch-dryer-wpa-dryer-abnormal-noise)
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
