This yellowish phlegm-like substance has been only his urates for a good two months now, since just after christmas. It doesn't look like liquid urine to me, honestly. I'm wondering if it's due to the diet change from mice to strictly rats, or if its a delayed reaction from some of the shots(injected amakacin, which is supposed to be hard on the kidneys) I gave him for a minor RI back in November. My vet said it was nothing to worry about on his last checkup, but it's just disturbing to look at for some reason.

Is this something someone could identify for me?

http://i39.tinypic.com/2e5l0r4.jpg