Help with my car..

I purchased my 2013 Honda Civic Si HFP coupe a month ago. I noticed that there was this hissing/boiling noise after I would drive it coming from my left side of the engine bay. My buddy also noticed I was losing coolant so we topped it at least twice. I brought it to a mechanic but said there was no leak and the car seemed perfectly fine. The noise disappeared and just today I noticed it came back. I checked the coolant level but is was right at max. The car has been somewhat modified. Its on coils, downpipe, short shifter, intake and a tune. Here is the clip I managed to get of the strange noise.
https://vimeo.com/461175197