I purchased a Bosch dishwasher SHU43C02uc/22

I purchased a Bosch dishwasher SHU43C02uc/22 about 4 years ago. Recently during the last 2 washes, the machine has been giving off a smell like hot rubber during the wash cycle. It otherwise runs perfectly (dishes are clean, drains okay, etc). I have done just the routine maintenance like checking for large pieces of food but have found nothing so far. Any suggestions as to where I should look for where the smell might be coming from?