A Bosch SHX78CM5N that makes a noise you did not hear before is easier to diagnose than most dishwashers because it is so quiet in normal use. This 800 Series model runs at about 42 dBA, so a rattle, a scrape or a hum stands out. Learn what is normal first. A soft whoosh of water, a low hum from the circulation pump, the click of the diverter moving between the upper and lower arms, and a gurgle as the drain pump empties the tub are all part of the cycle.
The checks in more detail
A faint mineral smell from the zeolite in the first weeks is also normal and has nothing to do with noise. A rattle or a knock usually comes from the load. A cup or a bowl tipped over, a utensil slipping through the third rack, a lid not clipped down or a rack not fully pushed in can all knock against the spray arms or the tub wall. Open the door mid-cycle, if safe, and listen, then move the item.
A scraping or a slapping sound as the arms turn usually means an arm is hitting a tall dish or the third rack; spin the arms by hand, reload so that nothing protrudes and lock the third rack in position. A rack with a worn wheel rattles as it slides, and a replacement is inexpensive. A louder hum, a grind or a rasp points to the pump area. Debris in the sump, a broken piece of glass or a bone can sit around the pump and make it grind.
Remove the filters, check the sump and clear any debris; refit the filters firmly. A loud buzz with no water movement and an E code can mean the pump is struggling against a blockage. If the noise is a high-pitched whine that began suddenly and rises with water flow, the circulation pump bearing may be worn, which a Bosch technician can check with the model and the FD number from the door plate. Level the dishwasher too, since a loose mounting amplifies noise through the cabinets.
Differential
Likely causes of “Bosch 800 Series SHX78CM5N dishwasher makes grinding, humming”, and how to tell them apart
- 1
A loose item in the load
What separates it A rattle or a knock
How to confirm Reload and secure small items
- 2
An arm hitting a dish or rack
What separates it A scrape as the arms turn
How to confirm Spin the arms by hand and reload
- 3
Debris in the sump
What separates it A grind from the base
How to confirm Clear the filters and sump
- 4
A worn rack wheel
What separates it A rattle as the rack slides
How to confirm Replace the wheel
- 5
A worn circulation pump
What separates it A whine that rises with flow
How to confirm Technician check
Before you touch a setting
Record this first — changing settings destroys the evidence
- When in the cycle the noise happens
- Whether it follows the arms turning
- Whether it changes when the load is rearranged
- The FD number on the door plate
Try in this order
0 of 6 completedLearn the normal sounds
ReversibleWhoosh, hum, click and gurgle.
Listen mid-cycle
ReversibleFind where the sound comes from.
Reload and secure items
ReversibleNothing protruding.
Spin the arms by hand
ReversibleThey must clear every dish.
Clean the filters and sump
ReversibleCheck for glass.
Call Bosch
ReversibleFor a pump whine or grind.
Model-specific
What is true of this model and not of its siblings
- Normal sounds
- A soft whoosh, a hum, a diverter click and a drain gurgle belong to every cycle.
- Load noises
- Loose items knock against arms and walls; secure them.
- The arms
- They must turn freely and not meet tall dishes.
- The sump
- Glass and bones cause grinding; clear them.
- Pump wear
- A whine that rises with flow points at the circulation pump.
- Bosch help
- Quote SHX78CM5N and the FD number.
Stop boundary
When this stops being a self-service repair
- !Do not run the dishwasher with broken glass in the sump
- !Switch off before reaching into the base
- !Call Bosch for a grinding that continues with an empty tub
Evidence ledger
Sources behind this answer
Exact questions
Common questions
Why does my quiet Bosch suddenly sound loud?+
At 42 dBA any new sound stands out; check the load first.
Is a click normal?+
Yes, the diverter moves between the arms.
Is a gurgle normal?+
Yes, when the drain pump empties.
What does a grind mean?+
Debris around the pump.
Can I fix a rack wheel?+
Yes, it is an inexpensive part.
Will levelling help?+
Yes, a loose mounting amplifies noise.