On the 7th fret of my D string it makes a buzzy rattling sound but ive checked every fret on every string and no others do it. Is there anything I can do to fix this at home I want to start fixing stuff myself and it's only a cheap guitar so I'm not worried.

It's a clammy rattly buzzy sound. And it almost stops the note ringing.
It is 1 of two problems that are both fixed in similar ways

Most likely cause is that your 8th fret has started to lift slightly so when you push on the 7th fret the string actually chokes on the 8th fret. Sometimes this can be fixed by lightly tapping the 8th fret down with a plastic, wooden, or brass hammer. Even hitting it with the back of a screwdriver could do the trick. Don't use a regular steel hammer because that will damage the fret. If tapping the fret lightly doesn't fix it then you will have to grind the fret down. I like to use a large sharpening stone like you would use to sharpen a chisel pocket knife. There are tutorials online on fret leveling so I'm not going to give a full explanation here.

The other possible problem is that your 7th fret is too low. This requires you to grind down the frets using a sharpening stone like I mentioned before, however, it probably means you will need to grind down all the frets to match your low 7th fret which generally means more grinding that if you had a high 8th fret. Because you are going to be grinding more off all the frets you are also going to need to crown the frets and I would suggest getting a fret file from LMI to do that. They are relatively inexpensive and are much easier than recrowning the frets with tools from your local hardware store.
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I just found out I get it on 2 other frets but it's only when picking/strumming hard to get more sound. Kinda annoying me now. So definatelly frets? I've never adjusted truss wouldn't loosening a little help or should I try tapping frets on first.
I tapped it a bit and it's helped not perfect but better might unwind strings tomorrow and tap them back in if any are out. Is it normal to have some buzzing when playing harder?
buzzing when you play hard is normal. Truss rod adjustments only helps on lower frets so if the buzzing frets are 7th fret and lower then there is a chance loosening the truss rod could help but it's also possible that it is uneven fretwork and the frets need leveling.
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I have a buzzing fret on the 4th fret of the G-string on my washburn. Adjusting the truss rod took away nearly all of it. Only buzzes a tiny bit now and only if I pluck that note really hard.

Your guitar probably just needs a truss rod adjustment. You do this by placing a capo on the first fret and holding down the low e-string @ the 14th fret. Then you measure the clearance between the low e-string at the 6th fret using a feeler gage. You want to have .010 in. of clearance. Loosening(turnleft) increases the clearance. Go about 1/4 turn at a time. You can use a business card to measure if you don't own a set of feeler gages. There are many different tutorials on adjusting truss rods if you do a google search. It's not difficult but you'll want to look over a few different instructions until you feel comfortable if you've never done it before. My guitars all use a 5/32 allen wrench to adjust the truss rod.