hissing

This week I purchased 2 male guinea pigs. I've spent a couple months prepping, researching and planning to make sure I am doing the right thing. It's been 5 days now of me getting them settles and I've started to notice one of them (the most shy one - peanut) hissing every now and again...

Pipey and Nugget both make strange sounds when I put my ear to them. It almost sounds like hissing! Is it normal for breathing to sound like that? It sounds like thhh, thhh, thhh. Pipey especially makes that sound.