Smell from 3 year old dental implant - no infection. What can cause this?

A bacterial infection may cause smell. It could be because of gum inflammation or inflammation in the tissue surrounding the implant. If your dentist has ruled out these tissues, you should pay extra attention to your oral hygiene. Food particles might be accumulating around the implant. You can use water flosser every night after brushing your teeth. This will significantly reduce the smell.

There are multifactors for that. so without a check-up, it's difficult to guide you.
but the main cause is food lodgement.
are you using water floss? if not, use that.
even after that smell, a check-up is a must.

A smell around a 3-year-old dental implant, even without infection, could be caused by food debris or plaque buildup beneath the crown or along the gumline. Implants require meticulous cleaning, as bacteria can accumulate in hard-to-reach areas around the abutment and crown. Consider using tools like an interdental brush, water flosser, or implant-specific floss to clean thoroughly around the implant. If the smell persists, it might indicate minor gum irritation or peri-implant mucositis, which is the early stage of gum inflammation around an implant. Visiting your dentist or periodontist for a deeper cleaning or evaluation could help resolve the issue.