asterisk users - Jul 2007 - choppy sound when transcoding (after os update)

after recompilling asterisk (trunk-r75109) after system (mandriva 
cooker) update (new glibc 2.6, gcc 4.2.1),
sound starts very choppy, when codec translation is performed,
if translation isn't needed, it sounds OK
any idea? until update, everything worked fine.
I'm using ztdummy as clock source.

during compile, I got lot of errors...

ael_main.c: In function ?ast_context_add_ignorepat2?:
ael_main.c:306: warning: passing argument 1 of ?create_name? discards 
qualifiers from pointer target type
ael_main.c: In function ?ast_context_add_switch2?:
ael_main.c:328: warning: passing argument 1 of ?create_name? discards 
qualifiers from pointer target type
ael_main.c: In function ?ast_context_add_include2?:
ael_main.c:317: warning: passing argument 1 of ?create_name? discards 
qualifiers from pointer target type
[CC] ast_expr2f.c -> ast_expr2f.o
ast_expr2.fl: In function ?ast_yyerror?:
ast_expr2.fl:376: warning: passing argument 1 of ?expr2_token_subst? 
discards qualifiers from pointer target type



chan_agent.c: In function ?__agent_start_monitoring?:
chan_agent.c:393: warning: the address of ?savecallsin? will always 
evaluate as ?true?
chan_agent.c:396: warning: the address of ?urlprefix? will always 
evaluate as ?true?
[LD] chan_agent.o -> chan_agent.so
[CC] chan_iax2.c -> chan_iax2.o
chan_iax2.c: In function ?iax2_prune_realtime?:
chan_iax2.c:2050: warning: passing argument 1 of ?expire_registry? 
discards qualifiers from pointer target type