Low pressure injectors (i.e. injectors that supply fuel into the intake ports) aren't normally that loud. I know direct injection injectors (like the ones in my wife's MKV GTI) are pretty loud. The Ultima hatch she had before that (ZZE-122R - 1ZZ-FE) had quiet injectors - same injection into intake port setup as your 2ZR-FE. Get it checked mate, just in case a lash adjuster has bunged itself in and causes consequential damage.
I reckon when Toyota bring out the Valvematic engines to replace the current VVT-i series, they'll go direct injection. Still about 3 years away I'd say...
itll be interesting to see.
if you want noisey injectors try the nissan rb30 theyre really loud