Medium prounanciation

The 'y' sound is not necessary but it naturally comes to most of us native speakers when '...ium' is used in a word. Pronunciation and linguistics are not my areas of study but it's probably a slight slurring of the 'i' and 'u' sounds to avoid a slight stop between them and a clear extra syllable.

If the 'y' is in place of the 'i' then it's simply a lazy way of avoiding pronouncing th

Hi

That's quite true. If I pronounce it (as a native speaker), my tongue touches the back of my top teeth and, just slightly, it sounds like 'medi - y -um'. If I try to pronounce it without doing that, it sounds OK but it doesn't feel that comfortable

I have to say that it's just a slight difference and people may say it either way. I don't believe there's a need to practice a

anonymousI hear y sound but there is no y in the spelling.

English spelling is not phonetic. You'll drive yourself crazy if you expect it to be. There are hundreds of examples like this.

I hear a Y sound in "beautiful" but there is no 'y' in the spelling.
I hear an R sound in "colonel" but there is no 'r' in the spelling.
I hear an F sound in

So do you prounance I followed by y as medi y um or without the I as med y um please .