I have 6 silkie chicks , one week old ( bought off craigslist). They are in a brooder in my garage. The brooder is wooden with a wire top and pine shavings as bedding. Ecoglow heater. Chickstarter feed and I keep their water fresh. Now to the problem.... they sound very "crackly " when they breath, some seem weak and shake their heads a lot . One died 2 days ago! What could it be & what should I do?????