Fox Mulder
The Truth Is Out There
Remember that when you introduce a highpass filter to audio even at 30hz, its going to cause a phase shift that will change the envelope of the original signal, causing higher peak levels. I'm not sure if this is such a desirable quality to bring to the table, but hey, if it makes it sound more dynamic, go for it.
That's why it's important to use linear phase eqs with such work.