Hello, I'm Dr. Deb and will do my best to help you today.
I'm sorry for this concern about Max. When one of my clients starts to detect a change in the odor of their cat's urine,, then I'd want to rule out a few conditions, even though the patient may not be acting differently or showing any other signs (such as increased thirst, urination or change in appetite or weight).
2. Kidney disease
3. Urinary tract infection
4. Possibly something else going on with the bladder such as a mass.
If Max was my patient, I'd want to check a urinalysis on him before anything else which will should help to narrow down the list. Then, depending on the results, blood work would probably be the next thing I'd want to do with an ultrasound an additional diagnostic test to consider if appropriate.
If this odor has only been present for a short period of time and he's not acting ill in any way, then I might continue to monitor the situation for a little while longer. I might also think about any diet changes recently which might account for the change in odor as well.
I hope this helps to provide possible explanations for what you're detecting. Deb