A lot of milk, particularly the extra filtered stuff, doesn’t seem to smell when it goes off anymore…the first you know is the taste or when it curdles when added to a cuppa.
I realised this a while a go, as I work out of a van all day I keep my milk in a coolbag now and take it home to put in the fridge at night. A colleague has just started following my approach, he used to just keep in in the van overnight and use the sniff test each morning…thats until he swigged a mouthful of sour milk recently and sprayed it back out all over the inside of the van 😆
I bought a pint of gold top as it had been reduced to 20p with a day left, luckily I took a swig before ruining my coffee…even though its not filtered it tasted sour but had no bad smell.
Get a temperature gauge for your fridge, the thermostat could be dodgy.